ROOF TOP SOLAR SOLUTIONS FOR URBAN OFFICE/INDUSTRY BUILDINGS
Case: Statcon Energiaa Office Building, Sector 63, Noida
Typically every building be it office, factory, nursing homes, dentists, Labs, Malls, schools, factories etc. Needs to run on electricity and uses DG Set as a backup source for daily usage. This is because the condition of grid supply is erratic and suffers from frequent interruptions of different sizing which may be termed as blackout or brown outs. In addition to it, the cost of fuel as well as electricity is going up and adding only renewable sources like solar/wind may not be enough due to their unpredictable nature.
Therefore a true solution lies in creating a buffer which is bidirectional and can stand and deliver the energy reliably in a most cost effective manner.
Case Study: Newly constructed Office of Statcon Energiaa is to be constructed as a modern office with all amenities and at the same to prove as model for all other buildings aiming to go green.
- Erratic Supply and poor quality of Grid
- Ever increasing cost of diesel and maintenance of Diesel Generator Sets
- DG Set running at less than 30% rated capacity causing a decrease in life of the DG Set
- Loss of productivity among employees
- A sun exposed terrace causes extra strain on the Air conditioners
- Frequent power cuts of 10 minutes to 4 Hours
- Increasing cost of electricity with Time-Of-Day (TOD)
- Very High fixed charges bringing the electricity bill to > ₹ 9.50 Per Unit ($ 0.14 per unit)
- Typically the peak load does not end at 4 pm and electricity charges can be as high as 15-20% in this TOD of 5pm- 10pm regime.
Method:5 Things were to be considered before designing the Solar Power System.
- Aesthetics of the building
- Extra space utilisation of the terrace
- Ergonomics of the installation keeping future maintenance in mind
- Type of inverter system to cater to sensitive server loads and increasing diesel costs
- Payback period
With discussions between the architect and the design team, an angled tin roof was constructed upon which the solar panels were installed with a total capacity of 30KWp. A metal mesh to walk about was also put up for cleaning purposes.
- PV Panels: 30KWp
- Inverter: 100 KWp
- Type of Inverter System: HYBRID Grid Synchronised (ON GRID /OFF GRID)
- Battery Capacity: 240V/ 300Ah
- Air Conditioners: Casette + Split Type
- LED Lights
- Coffee Machines
Total Peak Load = 45 KWp
Special Features of the System:
- Hybrid Inverter ensures that the battery is at peak charge condition whenever it is called upon.
- Maximum amount of savings is ensured by TRUE POWER SHARING between multiple sources in a prioritised manner. This is done as shown in the *block diagram* shown. The Solar panel is given the first priority to run the primary and secondary loads and only the deficit that the solar is unable to supply is taken from the grid.
- On Sundays and National Holidays when the Office is closed, the Inverter can export the excess power to the Grid which with the added bonus of net metering allows the owner for a faster payback period on the Solar System.
- With the above mentioned scheme, Statcon Energiaa is also set to become the first entity in NOIDA to be allowed for Exporting to the grid.
- Apart from this backup generators are also kept as an emergency backup, which can switch on automatically by the inverter if all the other 3 sources of power fail to supply the load. But giving credit to the System, the DG Set has only been switched on twice in the past one year. And that too on days of continuous rainfall during the monsoons.
- Batteries can be charged according to the Time of Day. Electricity charges are different according to the TOD in UP and thus the batteries can be charged via grid during the night when rates are low and utilised during the day time when rates skyrocket, again reducing the payback period
- A special feature in the inverter is the Night saving mode, here the inverter shuts down at 8PM all working days to cut off the transformers from consuming no load magnetising current, which can amount to more than 2KW after hours. The Inverter will switch ON after 12 seconds when the grid does go down but otherwise stay shut down till morning 8AM
The extra space thus obtained on the roof is being utilised by two cabins, one canteen area with 10 tables and a capacity for seating about 60 people, a corner for the Inverter + Battery System and a showroom to showcase the company products.
Picking the Type of Solar system:
- Grid Tie System: A grid tie system is one in which the inverter output synchronises with the grid connection and feeds directly to the load without any storage medium in between. It is cheaper than hybrid and smaller in size as well. But the major problem in this is that it will not produce electricity when the grid is absent, even when the sun is shining merrily, due to anti islanding of the system. This meant that our Diesel consumption would not go down even by one bit. A turn around to the problem was that the DG will be switched ON and the inverter output would synchronise to the DG output when the power is down. But the deal breaker condition is that :
#1 you are not saving any diesel
#2 as the inverter output is supplying most of the load and the DG set we had would therefore run at a capacity of less than 30%, it would result in a carbon and soot build up inside the DG SET mechanism causing it run much inefficiently and reduce its life period.
#3 Also switching ON the DG set would require a couple minutes and even that would interrupt our sensitive server loads plus the LOSS in productivity.
- Off Grid System:
Simpler of the three systems, it uses Solar to serve the primary loads and charge the battery when PV is present while Grid is used to supply rest of the loads. When solar is down, then grid takes command over the entire load as well as the charging of the battery system. In case The grid is down then Battery + Solar supplies the load and if the PV is down as well then the responsibility shifts to the battery alone.This is a simple enough system that most of us are familiar with due to its availability for long. But a major drawback of the system is that it is not the best system for the battery life and batteries are AFTER ALL the most expensive components of the entire system.
Thus the off grid system was discarded (although one unit of 6kVA still functions as a UPS to the server)
- Hybrid System:
Thus comparing the features of the above two systems with those mentioned above for Hybrid systems we felt that for our case, even though the other two have their own benefits, the Hybrid system would be the most suitable and more beneficial in terms of utility and a faster payback period.
- Initial Investment:
PV Panels: 250×120= 30KW= 11,42,400 ₹
Inverter: 100kVA= 9,23,950 ₹
Batteries: 2Vx120 /300Ah = 5,83,000 ₹
Mounting structure= 73,200 ₹
Installation and commissioning= 60000 ₹
TOTAL= 28,00,500 ₹
- Savings & Payback Period =
Per unit cost of electricity= 9.86 ₹
Per unit cost of DG, electricity=22.83 ₹
(Note: we are considering 70% from electricity and 30% from DG for per unit cost)
Total energy generated by solar per year (units) = 46530 units or KWH
Total savings per year ( in rupees) = 632436 ₹
Project cost: 2800500 ₹
Payback period will be around year= 4.43 years
- Hidden Savings:
a) Night Sleep Mode: As mentioned above the night sleep mode has resulted in hidden savings which when calculated amount to savings of more than 50,000₹ per annum.
b) Employee Productivity: Frequent power cuts cause the shutdown-restart delay of computers, loss of concentration, and a general loss of productivity which cannot be measured in terms of money. All this is avoided by an un-interrupted supply.
c) Lesser load on ACs: The Sun rays falling directly on the terrace causes it to heat up and increase the pressure on the air-conditioners cooling the floor below. The solar panels structure causes it to naturally bring down the temperature by providing shade.
d) No more Diesel Pilferage: A lot of human effort to bring (transport costs) and store (storage space) the diesel whilst ensuring that theft does not occur (precious man-hours) was required earlier. Not anymore.
e) Exporting to the grid through net metering: Once the State electricity board allows for Grid export then Holidays, lean load days and winter days will result in a faster payback period through the feature of grid export via net metering.